Attenuation of Eye Movements Evoked by a Vestibular Implant at the Frequency of the Baseline Pulse Rate

We are developing a vestibular implant to electrically stimulate vestibular neurons in the semicircular canals in order to alleviate vertigo, which is a commonly occurring problem. However, since electrical stimulation causes synchronous (phase-locked) neural responses, such electrical stimulation might also cause inappropriate vestibuloocular eye movements, which might, in turn, cause visual blurring. We investigated the eye movements evoked in the guinea pig using electric stimulation with a constant rate of 250 pulses per second (pps), and measured 0.010
$^{\circ}$
peak-to-peak eye movements on an average at 250 Hz, with an average peak velocity amplitude of 8.1
$^{\circ}$
/s, which might cause visual blurring. However, after half an hour of stimulation, that component reduced to 1.6
$^{\circ}$
/s (0.0020
$^{\circ}$
peak-to-peak). The average time constant for this reduction was 5.0 min. After one week of constant stimulation, the 250-Hz response component was only slightly smaller, at 1.2
$^{\circ}$
/s (0.0015
$^{\circ}$
peak-to-peak). We conclude that although an electrical prosthesis with a resting rate of 250 pps may cause some visual blurring when first turned on, such blurring is very likely to attenuate and be imperceptible within several minutes.